On Apr 12, 2009, at 21:58 , Timothy Hayes wrote:
I was wondering if someone might be able to shed some light on a
couple of questions I have.
When you receive a fragment/base_descriptor in a BTL module, is the
raw data allowed to be fragmented when you invoke the callback
function? By that I mean, I'm using a circular buffer in each
endpoint so sometimes data loops back around. Currently I'm doing a
two step copy: from my socket to the circular buffer and then from
the circular buffer to the fragment. This actually effects my total
throughput quite a bit, it would be much nicer to just point to the
buffer instead. When I tried using two base_segments to point to the
start and end of buffer I got some pretty strange errors. I'm just
wondering if someone could confirm or deny that you can or can't do
this, maybe those errors were down to human error instead.
On the descriptor you can set a number of iovec containing the raw
data. You don't have to make it contiguous prior to calling up in the
PML. I think the PML header has to be contiguous, so you have to make
sure that the first 32 bytes of the message are contiguous.
My other question is about the BTL failover system. Would someone
be able to briefly explain how it works or maybe point me to some
docs? I'm actually expecting the file descriptors in my module to
fail a certain point during an Open MPI job and I'd like my BTL
module to fail gracefully and allow the TCP module to take over in
its place. I'm not sure how to explicitly make the the BTL module
say to the rest of Open MPI "don't use my anymore" though.
There is no way to say don't use me "at all" anymore. This is per peer
based, so you will have to return an error on every peer. Try
returning OMPI_ERR_OUT_OF_RESOURCE from all functions that allocate
descriptors (_alloc, _prepare_src and _prepare_dst), and the PML will
end-up removing this BTL from the list.
george.
Happy Easter
Tim
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